Mergers and Acquistions - Intangible Assets (Details) - Express Scripts Holding Company [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Acquired Intangible Assets [Line Items]
Total	$ 41,168
Customer relationships [Member]
Acquired Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 30,210
Customer relationships [Member] | Minimum [Member]
Acquired Intangible Assets [Line Items]
Estimated useful life	14 years
Customer relationships [Member] | Maximum [Member]
Acquired Intangible Assets [Line Items]
Estimated useful life	29 years
Internal-use software [Member]
Acquired Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 2,443
Internal-use software [Member] | Minimum [Member]
Acquired Intangible Assets [Line Items]
Estimated useful life	3 years
Internal-use software [Member] | Maximum [Member]
Acquired Intangible Assets [Line Items]
Estimated useful life	7 years
Trade Name [Member]
Acquired Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 115
Indefinite-lived Intangible Assets Acquired	$ 8,400
Trade Name [Member] | Minimum [Member]
Acquired Intangible Assets [Line Items]
Estimated useful life	10 years